1. Field of the Invention
The invention relates to a cylindrical alkaline storage battery suitable for increasing capacity thereof.
2. Description of the Related Art
As alkaline storage batteries, there can be mentioned, for example, a nickel-cadmium rechargeable battery, a nickel-hydrogen rechargeable battery, etc., which contain different active materials. Among these alkaline storage batteries, there are cylindrical ones having a cylindrical outer can that accommodates therein an electrode group formed by strip-shaped negative and positive electrodes that are spirally wound, with a separator interposed therebetween.
In this type of cylindrical alkaline storage battery, the negative electrode is made larger in capacity than the positive electrode so as to reduce oxygen gas produced in overcharging, thereby preventing the inner pressure from increasing. In order to increase the battery capacity, it is required to increase the amount of a positive-electrode active material. To meet this requirement, various proposals have been made.
For example, a cylindrical alkaline storage battery is disclosed in Japanese Unexamined Patent Publication No. Hei 4-206474, in which that part of the negative electrode which forms the outermost circumference of the electrode group and which contributes little to battery reaction is made smaller in thickness than the other part. It is thought that the battery disclosed in Japanese Unexamined Patent Publication No. Hei 4-206474 is arranged to decrease the thickness of part of the negative electrode forming the outermost circumference of the electrode group, thus increasing the volumetric efficiency to achieve high capacity
However, the cylindrical alkaline storage battery disclosed in Japanese Unexamined Patent Publication No. Hei 4-206474 can produce cracks and/or splits in the thin part of the negative electrode which forms the outermost circumference of the electrode group. This poses a problem of part having a crack and/or a split piercing through the separator and coming in contact with the positive electrode to produce a short circuit, and another problem of the electrical resistance being increased in the aforementioned part to increase the internal resistance of the storage battery, allowing the storage battery to abnormally heat during charging and discharging.